L-threonine, which is one of natural amino acids, is widely employed as feeding materials and food additives as well as a raw material for the synthesis or production of rehydration solution or other medicines. D-threonine and D- or L-allo-threonine are unnatural amino acids and can also be considered as useful chiral building blocks.
Threonine having a general name of 2-amino-3-hydroxy-butyric acid has two chiral centers at 2-position and 3-position in its molecule and thus has 4 stereoisomers including, specifically, L-(2S,3R)-threonine (Formula 1), D-(2R,3S)-threonine (Formula 2), D-allo-(2R,3R)-threonine (Formula 3) and L-allo-(2S,3S)-threonine (Formula 4) as follows:

A reference article [Organic Syntheses, Coll. Vol. 3, p. 813 (1955); Vol. 20, p. 101 (1940)] discloses a preparation of D, L-threonine in a racemic form containing all 4 isomers through all 8 steps from crotonic acid as the starting material.
Korean Patent Laid-Open Publication No. 2003-0036199 discloses an enzymatic preparation of natural amino acid of L-threonine using Enterobacters. In addition, methods of preparing L-threonine by an enzymatic method via gene recombination are disclosed in several patents and references.
A reference article [Tetrahedron: Asymmetry Vol. 2, No. 1, pp. 555-561. 1991] discloses a stereoselective preparation of D-threonine and L-threonine using a ruthenium catalyst.
U.S. Pat. No. 4,211,840 discloses a preparation of D-threonine by using a microorganism or an enzyme, which comprises cultivating a microorganism that uses a hydantoin derivative as a nitrogen source and contacting the cultivated microorganism with various hydantoin derivatives to prepare several type of D-amino acid including D-threonine. However, there is a problem that the yields in most of Examples of said patent do not exceed 50%.
WO 01/40450A1 discloses a preparation of chiral alcohol compounds which are a raw material of a hyperlipidemia treating drug by reducing a ketone compound using a reductive enzyme.
A know reference [Helv. Chim. Acta vol 70; 232-236, 1987] disclosed a preparation of L-threonine by reducing a ketone using a microorganism, but there may be problems that the commercial viability is low since the yield is very low, for example about 16%, and that side products that are difficult to be separated are simultaneously generated.
As such, there has been necessity for a method of preparing economically and in a high yield D-threonine and L-allo-threonine which are expensive amino acids and importantly employed in new drug development and chemical synthesis.
Meanwhile, research has been largely performed on the preparation of expensive amino acids by an enzymatic reduction using a microbial reductive enzyme to prepare expensive amino acids which can be importantly employed in new drug development and chemical synthesis. However, although there have been many researches on the preparation of chiral alcohol by an enzymatic reduction, there is little research on the preparation of chiral amino acids.
In enzymatic reduction methods, genes corresponding to reductive enzyme are separated from microbials which are novel microbials isolated from natural world or which are known in articles or patents, said genes are transferred into a plasmid and then transformed in E. coli, which is cultivated. Said cultivated E. coli is separated and employed in an enzymatic reaction. In another way, said cultivated E. coli is broken and centrifuged to obtain a supernatant, which is used in the enzymatic reaction.